In the formation of integrated circuits, thin films containing metal elements are often deposited on the surface of a substrate. These thin films provide conducting and ohmic contacts in the circuits and between the various devices of an integrated circuit. For example, a desired thin film might be applied to the exposed surface of a contact or a via on a semiconductor wafer with the film passing through the insulative layers on the wafer to provide plugs of conductive material for the purpose of making interconnections across the insulating layers. There are a number of different conductors and insulators which are chosen for various purposes in an integrated circuit. These may include titanium, titanium nitride, titanium tungsten alloys, tungsten, aluminum, silicon dioxide, as well as many others.
Titanium nitride is used in a variety of applications for integrated circuit fabrication. It is used as an adhesion layer for tungsten films, as a total interconnect and as a diffusion barrier. As an adhesion layer, titanium nitride offers advantages and applications where blanket tungsten is used for contact hole and via filling. The process is normally started by depositing a thin layer of a material that acts to improve adhesion between the tungsten and the underlying dielectric. Since tungsten adheres poorly to dielectric materials, a material must be used which adheres well to the dielectric and then adheres well to the tungsten. There are several materials that are suitable, but titanium nitride has several advantageous properties such as very low resistivity and a resistance to the chemistries used to etch tungsten, as well as exhibiting good adhesion to both dielectric and tungsten films.
As a barrier layer, titanium nitride also offers advantages as it serves as an impermeable barrier to silicon. It also has an activation energy higher than other materials. For example, the activation energy for copper diffusion into titanium nitride is reported to be 4.3 eV, while the activation energy from copper into most metals is on the order of 1-2 eV. There are several different methods typically used to form a layer of titanium nitride. These can include evaporation of titanium in a nitrogen atmosphere, reactive sputtering of titanium in a nitrogen/argon mixture, sputtering titanium nitride from a target in an argon atmosphere, depositing titanium and then converting it to titanium nitride in a subsequent nitridation step, or thermal chemical vapor deposition reactions employing titanium tetrachloride and ammonia.
There are many unique concerns with each of these different methods, particularly exposure to high temperatures normally related to traditional thermal chemical vapor deposition processes. At the device level of an integrated circuit, there are shallow diffusions of semi-conductor dopants which form the junctions of the electrical devices within the integrated circuits. The dopants are initially defused using heat during the diffusion step. The dopants will continue to diffuse when the integrated circuit is subjected to high temperatures during chemical vapor deposition. Temperature limitations may become even more severe if thermal chemical vapor deposition is performed after metal interconnection or wiring has been applied to the inner integrated circuit. For example, many integrated circuits utilize aluminum as an interconnection metal. However, various undesirable voids and extrusions occur in aluminum when it is subjected to high temperatures. Therefore, once interconnecting aluminum has been deposited onto an integrated circuit, the maximum temperature to which it can be exposed is approximately 500.degree. C. and the preferred upper temperature limit is 400.degree. C.
Two pending applications, Ser. Nos. 08/253,366 and 08/263,393, both entitled "Method and Apparatus for Producing Thin Films By Low Temperature Plasma-Enhanced Chemical Vapor Deposition Using a Rotating Susceptor Reactor" and both filed Jun. 3, 1994, describe methods and apparatuses for producing thin films by low temperature plasma enhanced chemical vapor deposition using a rotating susceptor reactor suitable to apply by chemical vapor deposition techniques a thin layer of titanium nitride. Titanium nitride, however, frequently needs further post-treatment in order to be suitable for further use.